Cylinder head limit switch assembly



Dec. 3, 1968 WATSQN ET AL 3,414,693

CYLINDER HEAD LIMIT SWITCH ASSEMBLY Filed April 29, 1966 TINDALE P. WATSON ATTORNEYS ROBERT. D. V ENBURGH @bnzpvu/ United States Patent 3,414,693 CYLINDER HEAD LIMIT SWITCH ASSEMBLY Tindale P. Watson and Robert D. Vandenburgh, Jackson, Mich., assignors to The Tomkins-Johnson C0., Jackson, Mich., a corporation of Michigan Filed Apr. 29, 1966, Ser. No. 546,286 6 Claims. (Cl. 20082) The invention pertains to expansible motor apparatus and particularly relates to a cylinder head assembly incorporating a limit switch and actuator.

Expansible chamber motor devices of either the compressed air or hydraulic type, wherein relative axial movement occurs between a sylinder and a piston member located therein, are often controlled by electric switches. In the incorporation of expansible chamber motors in many applications, the control for such motors often includes electric solenoid valves which are operated by switches sensing the position of the motor piston, for instance. The machine designer, when incorporating a limit switch control with an expansible chamber motor device, usually mounts a switch abutment directly on the motor piston structure or on structure motivated or actuated by the movable expansible chamber motor element. An electrical switch is placed within the path of movement of the abutment whereby the abutment is capable of actuating the switch in response to the position of the movable motor component. While the location of the limit switch and its abutment is often determined by the apparatus involved, there are a large number of installations wherein standard limit switch actuating means are practical and desired. For instance, in the utilization of expansible chamber motors, it is very common to desire limit switch actuation upon the completion of the full stroke of the motor.

While there has been some development work done with built-in limit switch actuators for expansible chamber motor devices, such as that shown in United States Patent 2,960,077, previous limit switch actuators which form a permanent part of the expansible chamber motor have proved expensive, troublesome and incapable of withstanding the shock, impact, vibration and adverse conditions under which such built-in" limit switch actuators are subjected.

It is an object of the invention to provide an expansible chamber motor apparatus having a built-in limit switch actuator which indicates the extreme movement of a piston within a cylinder and wherein the apparatus is ecocomical to manufacture, yet is capable of withstanding the adverse conditions to which such devices are exposed.

Another object of the invention is to provide an expansible chamber motor apparatus incorporating a builtin switch actuator wherein the switch actuator forms a part of the support for the switch mounting bracket and a close, unitary assembly between the switch actuator, the switch support and the switch, itself, is provided.

A further object of the invention is to provide an expansible chamber motor apparatus wherein a limit switch actuator is formed as a part of a cylinder head and wherein passage means are associated with the limit switch actuator to prevent any leakage of pressurized fluid into the actuator from adversely affecting the actuator operation.

An additional object of the invention is to provide an expansible chamber motor apparatus employing a limit 3,414,693 Patented Dec. 3, 1968 ice switch actuator having a casing formed with an exteriorly threaded surface, whereby the threaded surface provides the means for retaining the actuator within the cylinder head and also forms the means whereby limit switch support structure may be mounted to the actuator and upon the cylinder head.

These and other objects of the invention arising from the relationships and details of components of embodiments of the invention will be apparent from the following description and accompanying drawing wherein:

FIG. 1 is a sectional, elevational view of an expansible motor cylinder and piston and associated head incorporating the limit switch and actuator thereof in accord with the invention, for use with expansible chamber motors employing a pressurized hydraulic fluid,

FIG. 2 is an enlarged, detail, elevational, sectional view of the limit switch actuator of FIG. 1 shown in the switch actuating position, and

FIG. 3 is a detail, elevational view of an embodiment of the invention, wherein the expansible chamber motor employs a pressurized gas such as compressed air.

FIG. 1 illustrates a typical relationship of components of an expansible chamber motor employing the concept of the invention. The motor includes a cylinder having an end closed by a head 12 mounted thereon by tie rods or other conventional head-mounting means. Piston structure is reciprocably mounted within the cylinder 10 and includes a piston 14 and piston rod 16 having enlarged cushioning projections 18 defined thereon adjacent the piston. In the illustration of FIG. 1, the head 12 is that head through which the piston rod extends.

The head 12, preferably, includes structure for cushioning the movement of the piston 14 as the piston approaches the head. Such cushioning structure includes a cylindrical orifice 20 concentrically related to the axis of the piston having an annular valve ring 22 located therein. The orifice 20 communicates with a chamber 24 and port 26 to which a supply and exhaust conduit, not shown, may be connected. As the piston 14 approaches and nears the head 12, the right projection 18 will be received within the orifice 20 and cooperate with valving 22 preventing escape of the exhausting hydraulic fluid through the orifice 20 and the chamber 24, and the fluid trapped between the piston and head 12 will cushion the movement of the piston toward the head. The trapped fluid is bled into the chamber 24, or port 26, by suitable bleed or throttle means, not shown. This type of operation is typified in the assignees United States Patent 2,719,510. The head 12 includes a gland 28 which seals the piston rod with respect to the head to prevent the leakage of fluid from the motor.

Head 12 is provided with flat exterior surfaces such as that at 30 and a radially disposed opening 32 is formed in the head which intersects the exterior surface 30 and terminates short of the inner surface 34 of the chamber 24. The opening 32 is defined at its bottom by a radial shoulder 36 and a radial shoulder is defined at 38. Threads 40 are formed in opening 32 from the shoulder 38 to the exterior surface 30.

A radially extending, cylindrical bore 42 is defined in the head 12 coaxial with the axis of the opening 32 and is formed with an inner end which intersects the chamber inner surface 34 for communication with the chamber 24, and the outer end of the bore intersects the radial shoulder 36. A seal-receiving recess 44 is formed in the head at the intersection of the bore 42 and the shoulder 3 36. As will be apparent from FIGS. 1 and 2, the diameter of the bore 42 is considerably less than the diameter of the opening 32.

A cylindrical casing 46 is received within the opening 32. The casing is exteriorly provided with threads 48 adapted to mate with the threads of the opening, and the axial length of the casing 46 is considerably greater than the axial depth of the opening 32, whereby when the lower end 50 of the casing is disposed adjacent the radial shoulder 36, the upper or outer end of the casing substantially extends beyond the head exterior surface 30.

Internally, the casing 46 is provided with a concentric, cylindrical chamber 52 which intersects the casing lower end 50. The chamber 52 is of a diameter greater than the diameter of the bore 42 and terminates at its outermost end in a radial face 54 axially spaced from the end 50. The casing outer end 56 is provided with a bore 58 of a diameter less than that of the chamber 52 which is coaxial with the chamber and intersects the chamber at the face 54. The outermost end of the bore 58 intersects the outer end of the casing, whereby the chamber 52 and bore 58 define an axial passage through the casing.

An annular washer 60 is received within the opening 32 and rests upon the radial shoulder 36. The inner end 50 of the casing is provided with small radial passages 62 which communicate with clearances 64 defined in the periphery of the washer 60 whereby a fluid passage is established between the innermost portion of the chamber 52 and the periphery of the washer for a purpose which will be later described. The washer 60 serves as a retainer for sealing means located within the recess 44 and also serves as an abutment for the flange of the plunger, as will be apparent later.

A plunger 66 is reciprocally mounted within the casing 46 and bore 42. The plunger includes a cylindrical inner end portion terminating in an inner end 68 having beveled edges. The plunger inner end portion is dimensioned so as to be closely, yet slidably receivable within the bore 42. An annular flange 70 is defined upon the plunger 66 about the configuration thereof adjacent the inner end portion. The flange 70 includes an annular groove 72 in which an O-ring seal assembly 74 is mounted. The flange 66, in the embodiments of FIGS. 1 and 2, is dimensioned relative to the chamber 52 so as to form a piston therein, and a sealed, sliding relationship between the plunger flange and the chamber is produced by the O-ring assembly.

The outermost portion of the plunger 66 is of a reduced diameter which is capable of axial sliding movement through the bore 58 and terminates in an outer end 76. The overall length of the plunger from the inner end 68 to the outer end 76 is greater than the distance from the chamber inner surface 24 to the casing outer end 56, as will be apparent from FIGS. 1 and 2. A seal 79 mounted on the plunger outer portion seals the plunger with respect to bore 58.

A compression spring 78 is located within the chamber 52 interposed between the chamber face 54 and the flange 70. The biasing force exerted by the spring 78 tends to bias the plunger 66 to its innermost position, as represented in FIG. 1. As shown in Fig. l, the normal position for the flange 70 is in engagement with the washer 60 due to the biasing action of the spring.

The support for the limit switch preferably consists of a rectangular housing 80 which employs a removable cover, not shown, whereby the limit switch may be completely enclosed within the housing. The housing includes a mounting opening 82 defined therein which is of a diameter slightly greater than the diameter of the casing 46, whereby the casing may extend through the housing opening such that the casing outer end 56 and the plunger end 76 will be located within the housing. A nut 84 threaded upon the threads 48 of the casing bears against the housing inner surface 86 and maintains the housing in firm engagement with the head exterior surface 30. A sealing O-ring 88 may be formed within a recess defined in the housing adjacent opening 82 to seal the housing against the entrance of moisture.

A limit switch 90 of the type commonly known as a micro switch is mounted within the housing upon adjustable mounting means 92 including a screw 94 and a housing mounted bracket 96, whereby the switch may be adjusted in a radial direction with respect to the cylinder 10 by inserting a screwdriver in the bracket notch 98. Tightening of the screw 94 firmly aflixes the position of the limit switch within the housing 80. The limit switch includes an actuator which is in coaxial alignment with the plunger 66 and is engaged by the outer end 76 of the plunger during switch actuation. The switch housing is provided with suitable access means for conductors at 102.

In the embodiment of FIGS. 1 and 2 wherein the pressurized medium introduced into the cylinder is a hydraulic fluid, an axial passage 104 is defined in the plunger 66 intersecting the inner end 68 thereof for communication with the chamber 24 and communicates with the casing chamber 52 through radial passages 106 at a location between the flange 70 and the face 54. The passages 104 and 106 thus establish communication between the chamber 24 and the chamber 52.

The area at the plunger inner end 68 subjected to pressurized fluid within the chamber 24 is substantially equal to the area of the flange 70 subjected to pressurized fluid within the chamber 52. Thus, the passages 104 and 106 equalize fluid pressure on opposite sides of the plunger flange 70 and eliminates movement of the plunger due to fluid pressure within the chamber 24.

In order to insure proper movement of the plunger 66 and in order to bleed off any fluid which may have seeped past the seal 44, whereby the plunger is able to quickly return to the normal position shown in FIG. 1, a passage 108 is defined in the head 12. At one end the passage 108 communicates with the atmosphere exterior of the head, and at the other end the passage communicates with the opening 32 adjacent the radial shoulder 36 and at the periphery of the washer 60. Thus, the clearances 64 provided on the periphery of the washer 60 permit any fluid trapped below the flange 70, when the plunger is in the operating position as shown in FIG. 2, to escape from the passage 108, as the plunger tends to return from the position of FIG. -2 to that of FIG. 1.

In operation, the plunger 66 will be in the normal innermost position shown in FIG. 1. In this position, the inner end 68 of the plunger wil be disposed within the path of movement of the right piston structure projection 18, and the projection is provided with a tapered surface 110, whereby as the piston 14 approaches the head 12 and the projection enters the chamber 24, the surface 110 will engage the plunger end 68 and lift the plunger, FIG. 2. Of course, raising of the plunger 66 will cause the plunger to actuate the limit switch actuator 100 and, upon a predetermined axial movement of the plunger, the actuator 100 will operate the contacts within the limit switch 90 to either open or close the limit switch contacts, depending on the type of limit switch employed. Thus, the limit switch 90 can be used to control any electrical device which is to be controlled upon termination of the movement of the piston 14 within the cylinder 10. When pressurized fluid is introduced into the port 26 to move the piston 14 to the left, as soon as the piston projection 18 disengages from the inner end of the plunger 66, the plunger will return from the limit switch actuating position of FIG. 2 to the normal position of FIG. 1. The resulting inward movement of the plunger will permit the limit switch contacts to return to the normal condition.

FIG. 3 illustrates an embodiment of the invention which is used with pressurized expansible chamber motors utilizing pressurized gases, such as compressed air. In the embodiment of FIG. 3, components similar to those previously described are indicated by primed reference numerals.

In the embodiment of FIG. 3, the bore 42' is shown to be of a greater relative axial length than that of the opening 32', and due to the difference in conditions between air and liquid operated cylinders, it is possible to somewhat vary the dimensional relationships of similar components between the embodiments of FIGS. 1 and 3. The casing 112 is substantially identical to the casing 46 and has a lower end which is adapted to directly engage the radial shoulder 36'. The casing 112 is provided with a chamber 52' and has a bore 58' formed at the upper end thereof coaxial with the chamber 52.

The plunger 114 is formed with a flange 116 adapted to directly engage the radial shoulder 36' at the normal position under the influence of the compression spring 78'. In order to prevent the escape of air between the plunger inner portion and the bore 42, an O-ring 118 is mounted within an annular recess refined in the inner end portion of the plunger.

The axial length of the casing 112 is such that the casing extends substantially beyond the exterior surface 30 of the head 12, whereby the limit switch housing may be mounted to the casing by the nut 84 in a manner identical to that of the previously described embodiment.

The plunger 114 is operated by the piston rod projection 18' in the manner previously described, and as the flange 116 does not have a sealing relationship with the chamber 52', and as air is being employed as the pressurized medium, it is not necessary in the embodiment of FIG. 3 to utilize pressure-compensating and bleed passage in the plunger or head, as in the previous embodiment.

Expansible chamber limit switch and limit switch actuating structure in accord with the invention has proved very dependable through many thousand cycles of operation. The fact that the inner end portion of the plunger 66 is firmly supported by the bore 42 throughout a substantial axial distance of the plunger inner end provides the plunger with a rugged and high strength mounting which resists the impact imposed on the plunger each time the piston projection 18 engages the plunger. The simplified construction of the casing and plunger and the minimizing of the number of components involved substantially reduces the opportunity of malfunction or disassembly due to vibration. In that the nut 84 serves to mount the housing on the head 12 and is directly associated with the casing 46, tightening of the nut serves as a locknut to also maintain the casing within the head opening 32. Thus, should the nut 84 become unloosened, the resultant looseness of the switch housing 80 will be readily apparent to the operator before damage is likely to occur to the casing, plunger, or other associated apparatus.

In the described embodiments, the limit switch and associated actuating apparatus is shown as mounted in the head of an expansible chamber motor through which the piston rod extends. The limit switch apparatus may be associated with either head of a cylinder and in many cases limit switch apparatus will be mounted on the head located at each end of a common cylinder.

In the described embodiments, the axes of the casing and plunger are radially disposed with respect to the axis of the piston rod. However, it is intended that the limit switch actuating structure may be mounted in the head such that the axis of the plunger and casing may be parallel, though offset, with respect to the piston rod axis. In such an arrangement, it is not necessary that a projection such as 18 be mounted on the piston structure. Instead, the plunger inner end portion may be of such length as to directly engage the piston as it approaches the associated head. In such an arrangement, the structure employed with respect to the limit switch and the casing, plunger, etc. is identical to that shown in the described embodiments.

While the plunger 66 will usually be employed to operate an electric switch, it is within the scope of the invention to substitute other types of switches therefor. For instance, a hydraulic valve could be positioned on the head 12, preferably mounted on the casing 46, for actuation by the plunger 66. Also, the structure of the invention mounted within the head has utility even though not employed with a switch in that the degree of extension of the plunger 66 from the casing 46 provides a visual indication as to whether or not the piston 14 is at its limit position relative to the associated head.

It is appreciated that various modifications may be apparent to those skilled in the art without departing from the spirit and scope thereof and it is intended that the invention be defined only by the scope of the following claims.

We claim:

1. Expansible chamber motor apparatus comprising, in combination, a cylinder having an end, a head enclosing said cylinder end and mounted thereon, said head including an exterior surface and an inner surface, piston structure reciprocably mounted within said cylinder, an actuating surface defined on said piston structure disposed toward said head whereby said surface is located adjacent said head inner surface upon said piston structure being located adjacent said head, a threaded opening defined in said head intersecting said head exterior surface, a smooth cylindrical first bore defined in said head coaxial with and intersecting said threaded opening and said head inner surface, a radial shoulder defined in said opening at the intersection of said opening and bore, said bore being of lesser diameter than said opening, a cylindrical casing having an inner end and an outer end and a threaded outer surface received within said threaded opening, said casing inner end being disposed adjacent said radial shoulder and said casing being of greater axial length than said opening whereby said casing outer end extends from said opening and projects beyond said head exterior surface, a cylindrical chamber defined in said casing coaxial therewith intersecting said casing inner end and defining a radial face disposed toward said casing inner end and axially spaced therefrom, said chamber having a diameter greater than that of said first bore, a second bore defined in said casing coaxial therewith intersecting said chamber face and said casing outer end, said second bore being of lesser diameter than said chamber, a plunger having a first cylindrical inner end portion reciprocally received within said first bore adapted to extend inwardly beyond said head inner surface, an enlarged circumferential flange reciprocably received within said chamber and an upper end portion reciprocably mounted within said second bore and adapted to extend therethrough, a compression spring within said chamber interposed between said face and said flange biasing said plunger toward said head inner surface, said plunger being of greater length than the distance from said head inner surface to said casing outer end whereby said plunger outer end extends from said second bore upon said plunger inner end being engaged by said piston actuating surface.

2. Expansible chamber motor apparatus as in claim 1, a limit switch support mounted on said head exterior surface having a mounting opening defined therein, said casing outer end extending through said mounting opening, a nut threaded on said casing outer end holding said support in engagement with said head exterior surface and a limit switch mounted on said support having an actuator in alignment with said plunger upper end.

3. Expansible chamber motor apparatus as in claim 1, wherein said flange normally engages said radial surface under the influence of said spring and said casing inner end engages said radial shoulder.

4. Expansible chamber motor apparatus as in claim 1,

wherein said plunger flange forms a piston operatively.

5. Expansible chamber motor apparatus as in claim 4, wherein a passage is defined in said head establishing communication between the atmosphere exterior of said head and said chamber adjacent said radial shoulder.

6. Expansible chamber motor apparatus as in claim 5, wherein an annular washer circumscribes said plunger and is received within said chamber in engagement with said radial shoulder, said casing lower end engaging said washer and said flange adapted to normally engage said Washer under the biasing force of said spring.

References Cited UNITED STATES PATENTS ROBERT K. SCHAEFER, Primary Examiner.

D. SMITH, Assistant Examiner. 

1. EXPANSIBLE CHAMBER MOTOR APPARATUS COMPRISING, IN COMBINATION, A CYLINDER HAVING AN END, A HEAD ENCLOSING SAID CYLINDER END AND MOUNTED THEREON, SAID HEAD INCLUDING AN EXTERIOR SURFACE AND AN INNER SURFACE, PISTON STRUCTURE RECIPROCABLY MOUNTED WITHIN SAID CYLINDER, AN ACTUATING SURFACE DEFINED ON SAID PISTON STRUCTURE DISPOSED TOWARD SAID HEAD WHEREBY SAID SURFACE IS LOCATED ADJACENT SAID HEAD INNER SURFACE UPON SAID PISTON STRUCTURE BEING LOCATED ADJACENT SAID HEAD, A THREADED OPENING DEFINED IN SAID HEAD INTERSECTING SAID HEAD EXTERIOR SURFACE, A SMOOTH CYLINDRICAL FIRST BORE DEFINED IN SAID HEAD COAXIAL WITH AND INTERSECTING SAID THREADED OPENING AND SAID HEAD INNER SURFACE, A RADIAL SHOULDER DEFINED IN SAID OPENING AT THE INTERSECTION OF SAID OPENING AND BORE, SAID BORE BEING OF LESSER DIAMETER THAN SAID OPENING, A CYLINDRICAL CASING HAVING AN INNER END AND AN OUTER END AND A THREADED OUTER SURFACE RECEIVED WITHIN SAID THREADED OPENING, SAID CASING INNER END BEING DISPOSED ADJACENT SAID RADIAL SHOULDER AND CASING BEING OF GREATER AXIAL LENGTH THAN SAID OPENING WHEREBY SAID CASING OUTER END EXTENDS FROM SAID OPENING AND PROJECTS BEYOND SAID HEAD EXTERIOR SURFACE, A CYLINDRICAL CHAMBER DEFINED IN SAID CASING COAXIAL THERE- 